This invention relates to various apparatus and processes found advantageous in the sustained supply of water as may be required in a humidification system, a life-support system, or the like. One aspect of the invention is a novel means for forming a pressure/vacuum seal between a flexible tubing and a rigid container.
Another type of apparatus disclosed in the art is that relating to the sustained feeding of moisture to sustain life. Among such devices are those disclosed in U.S. Pat. Nos. 3,753,315; 3,758,987; 2,183,970; 3,958,366; and the like.
Most of the liquid-supply devices are excessively cumbersome and expensive to produce, have relatively short sustained-watering duration, or are susceptible to having their water-feed sustaining means wholly or partially plugged. Indeed, most prior art devices present a combination of such problems to the user.
Capillary flow-inducing water-feed devices (which will be described below in connection with the most favorable water-feeding devices of the invention) have been known to the art. However, they have been deficient in operating characteristics for various reasons. For example, wick-type water feeders have such enormous areas exposed to the air that they lose too much water by evaporation before it is transported to the intended destination. One attempt to avoid this problem was to use a porcelain-type filter. However, since the filter had to be constructed in such a way as to avoid large, vacuum-breaking pores, it was constructed to have very small pores. Moreover, the length of the pores was relatively long because the pocelain required substantial thickness for mechanized strength. The consequence of the prior art construction utilizing such a ceramic material was that its total flow capacity was far too low to suggest the potential advantage of membrane-feed devices described herein.
It is another object of the invention to provide a novel polymeric or fiber-type microporous-membrane water-feeding apparatus, one which has an excellent combination of controlled pore size and thinness, to provide high water-feed rates and yet maintain a water-feed system free of air locking.
Still another object of the invention is to provide apparatus and process for growing mold, algae, fungi and the like.
Other objects of the invention will be obvious to those skilled in the art on their reading of this disclosure.
The above objects have been achieved by providing apparatus having a number of novel and advantageous features. In the first instance, the water-supply apparatus comprises a novel thin polymeric, microporous, membrane-feeding apparatus.
The apparatus of the invention more conveniently features a water supply device which is characterized by an ability to act as a thin capillary membrane to provide water to a designated situs and to draw water from a reservoir up through a tube. In filling such an apparatus, siphoning can be used. It has been found that a seal useful under pressure and vacuum can be readily formed to provide such a dual purpose seal between a rigid wall and a flexible tubing.
The thin porous membrane for use in the apparatus can be selected over a wide range of materials with particular attention given to the duration of time during which sustained, undisturbed growth of seedlings is required. However, in most embodiments of sustained watering apparatus disclosed herein, it will be of particular importance to restrict the thin porous polymeric or fiber-type membrane to one having a pore size characterized by a bubble point in excess of 4 inches of water, gauge, as is known in the porous-membrane art. In such situations, it is helpful to have a porosity bubble point of at least 4 inches of water; but more advantageously of from 12 inches to about 2 feet of water or more.
One favorable water-distributing polymeric membranes are those sold under the trade designation Microweb AW19 by Millipore Corporation of Bedford, Massachusetts. This membrane has a nominal 3-micron size. In general, pore sizes of from 0.05 micron to 10 microns are useful. Not only cast thin polymeric membranes, but also fabricated thin filament membranes are useful. Moreover, the material of construction is not important as long as the wetting characteristics and pore size allow a suitable capillary-flow rate and suitable bubble point. In general, the most advantageous membranes are less than 0.030 inch thick. Thus, useful thin membranes can be prepared from cellulose nitrate and acetate, polyvinylidene fluoride, polycarbonate, polyvinyl chloride and non-woven fiber (including inorganic fibers) with and without wetting agents.
Among the advantages of such membranes, in addition to their ability to provide water at high rates when needed, is the fact that, at pore sizes of below 3 microns, and especially below 0.2 micron, there is a significant exclusion of water-borne biological contamination such as small plants, bacterial and the like. This is believed to be of value as plant culture in general but it is of particular value in growing of sensitive plant life and especially of value in such harvest-oriented processes as fungi grown in preparative chemical processes, e.g. in preparation of pharmaceuticals and the like. In general, pore sizes below 10 microns are more useful than those having pore sizes between 10-20 microns.
The apparatus comprising a capillary-flow inducing filter of the present invention is particularly versatile because of such characteristics of the filter as: flexibility at all temperatures above the freezing point of water; better liquid transport capacity; freedom from any particulate residuals which are used in making some filters known to the art; greater reproducability during manufacture; less susceptibility; and greater ease in sterilizing.
Although cast polymeric membranes are preferred for most applications, it is also possible to use fibrous filters having appropriate characteristics. Such filters are manufactured by Pall Corporation, among others.
In the more favorable embodiments of the invention, the capillary filter of the invention is utilized in conjunction with a water-wicking distributor means which has a greater surface area than the membrane filter and assures distribution of liquid over a larger surface area than would be provided by the filter surface alone. Any wicking means suitable for a particular application may be selected; e.g. a highly wicking-absorbent paper would be useful. Indeed, flexible distributors are desirable to assure best contact with the membrane filter which itself is, advantageously, flexible to allow maximum choice in filter design configurations.